Continuous fiber reinforced aluminum matrix composites (CF-AMCs) offer exceptional specific properties when compared to conventional alloys and to particulate metal matrix composites. The longitudinal stiffness of such composite materials is typically three times that of conventional alloys, and the specific strength of such composites is typically twice that of high-strength steel or aluminum alloys. Furthermore, for many applications, CF-AMCs are particularly attractive when compared to graphite-polymer composites due to their more moderate anisotropy in properties, particularly their high strength in directions different that those of the fiber axes. Additionally, CF-AMCs offer substantial improvements in allowable service temperature ranges and do not suffer from environmental problems typically encountered by polymeric matrix composites. Such problems include delamination and degradation in hot and humid environments, particularly when exposed to ultraviolet (UV) radiation.
Despite their numerous advantages, known CF-AMCs suffer drawbacks which have hampered their use in many engineering applications. CF-AMCs generally feature high modulus or high strength, but seldom combine both properties. This feature is taught in Table V of R. B. Bhagat, "Casting Fiber-Reinforced Metal Matrix Composites", in Metal Matrix Composites: Processing and Interfaces, R. K. Everett and R. J. Arsenault Eds., Academic Press, 1991, pp. 43-82. In that reference, properties listed for cast CF-AMC only combine a strength in excess of 1 GPa with a modulus in excess of 160 GPa in high-strength carbon-reinforced aluminum, a composite which suffers from low transverse strength, low compressive strength, and poor corrosion resistance. At the present time, the most satisfactory approach for producing CF-AMCs in which high strength in all directions is combined with a high modulus in all directions is with fibers produced by chemical vapor deposition. The resulting fibers, typically boron, are very expensive, too large to be wound into preforms having a small-radius of curvature, and chemically reactive in molten aluminum. Each of these factors significantly reduces the processability and commercial desirability of the fiber.
Furthermore, composites such as aluminum oxide (alumina) fibers in aluminum alloy matrices suffer from additional drawbacks during their manufacture. In particular, during the production of such composite materials, it has been found to be difficult to cause the matrix material to completely infiltrate fiber bundles. Also, many composite metal materials known in the art suffer from insufficient long-term stability as a result of chemical interactions which can take place between the fibers and the surrounding matrix, resulting in fiber degradation over time. In still other instances, it has been found to be difficult to cause the matrix metal to completely wet the fibers. Although attempts have been made to overcome these problems (notably, providing the fibers with chemical coatings to increase wetability and limit chemical degradation, and using pressure differentials to assist matrix infiltration) such attempts have met with only limited success. For example, the resulting matrices have, in some instances, been shown to have decreased physical characteristics. Furthermore, fiber coating methods typically require the addition of several complicated process steps during the manufacturing process.
In view of the above, a need exists for ceramic fiber metal composite materials that offer improved strength and weight characteristics, are free of long term degradation, and which may be produced using a minimum of process steps.